Placement of catalytically active materials in combustion flames

ABSTRACT

Combustion of a carbonaceous fuel in a flame is improved by placing a catalyst comprising a metal or metal oxide in the primary reaction zone and thereby reducing smoke formation.

United States Patent [1 1 [111 3,925,001 Salooja Dec. 9, 1975 PLACEMENTOF CATALYTICALLY [56] References Cited ACTIVE MATERIALS IN COMBUSTIONUNITED STATES PATENTS FLAMES 2,014,686 9/ 1935 Lubovitch et al 44/4Inventor: Chander salooja Reading Taylor X England 2,828,814 4/1958Larkin, Jr. 2,855,770 10/1958 Grube 431/347 [73] Assgnea and EngneermgFOREIGN PATENTS OR APPLICATIONS Company, Linden, NJ. 1,067,642 5/1967United Kingdom 431/350 [22] Filed: Dec. 15, 1970 21 APPL 9 33 PrimaryExaminer-Charles J. Myhre Assistant ExaminerW1lliam C. AndersonAttorney, Agent, or Firm-Harold N. Wells; F. Donald [30] ForeignAppllcatlon Priority Data Paris Dec. 19, 1969 United Kingdom 61916/69July 29, 1970 United Kingdom 86707/70 [57] ABSTRACT Combustion of acarbonaceous fuel in a flame is img 431/4 431/347 proved by placing acatalyst comprising a metal or I n n u u u u e s s n l u I n e n l l I oe e s l l I u I e I l I I on t l I Field of ch IIIII u 326, 50, 351; meal oxide in the prlmary reaction zone and thereby reducing smokeformation.

7 Claims, 1 1 Drawing Figures US. Patent Dec. 9, 1975 Sheet 1 of 63,925,001

FIG. 7. P23 21 22 US. Patent Dec. 9, 1975 Sheet 2 of6 3,925,001

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US. Patent Dec. 9, 1975 Sheet 3 of6 3,925,001

US. Patent Dec. 9, 1975 Sheet 4 of 6 3,925,001

US. Patent Dec. 9, 1975 shw 5 of6 3,925,001

US. Patent Dec. 9, 1975 Sheet 6 of6 PLACEMENT OF CATALYTICALLY ACTIVEMATERIALS IN COMBUSTION FLAMES (all hereinafter termed smoke forbrevity) produced during combustion.

Carbon-containing materials such as natural gas, liquid petroleumhydrocarbons and solid carbonaceous fuels are combusted with air oroxygen to provide heat and/or power. In most instances of suchcombustion, efforts are made to derive thehighest combustiontemperatures by employing the minimum quantities of air (or oxygen) butin the interests of efficient utilization of the heat value of the fuel,it is necessary to provide an excess of air or oxygen over thestoichiometric requirement. The excess air lowers the temperature of thecombustion gases but ensures that the overall heat output is increasedand that the amount of non-combusted material which appears as smoke isreduced.

The smoke represents a wasted resource, is a potential ficult it is toeffect heat transfer from the combustion gases, in the case of boilersand furnaces, while in the case of heat engines, the thermodynamicefficiency is reduced. Among the proposals to reduce smoke, there may bementioned the use of additives in the fuel which pass with the fuel intothe flame, and pass through the flame: the additives or derivatives ofthe additivescan be detected in the resulting combustion gases, and insome cases contribute to the polluting nature of the combustion gases.

It is known in the art that all flames have a structure which can becharacterised as follows:

1. A cool zone at the base of the flame in which admixture of air andthe fuel takes place without substantial combustion of the fuel.

2. A very hot zone, termed the primary reaction zone, adjacent the baseof the flame in which combustion proceeds vigourously and in which theconcentration of ions is at a maximum in the flame.

3. A secondary reaction zone downstream of the primary reaction zonewhich contains the most luminous part of the flame.

Towards the downstream-end of the secondary reaction zone, smoketends tobe apparent especially when there is insufficient excess air.

It has now been surprisingly discovered, in accor materials will forconvenience hereinafter be termed catalysts.

Among the catalysts which are found to be useful are metals,- metaloxides and compounds which decompose under heat to metals and metaloxides, and metal salts which are substantially stable at hightemperatures. Specific examples of catalysts are barium, magnesium,iron, tin, aluminium, vanadium, manganese, sodium, calcium, zirconium,platinum, yttrium, lanthanum, erbium, gallium,.titanium, chromium,cobalt, nickel, palladium, rare earth metals other than thosehereinbefore specified, oxides of any of .the foregoing metals,compounds which decompose to oxides of the foregoing metals under theaction of heat, and heat stable compounds of said metals. It will beappreciated from the foregoing that many other metal compounds may beemployed.

It has also been discovered that materials which are in themselvescatalysts, in the sense herein intended, either having a weak or strongsmoke reducing effect, interact synergistically in a surprising andeffective way to enhance the reduction in smoke formation. Specificexamples of such synergistically effective combinations are the metals,oxides or heat stable compounds of: barium and sodium, barium andyttrium, barium and erbium, barium and zirconium, aluminium and sodium,aluminium and yttrium, aluminium and lanthanum, aluminium and erbium,aluminium and platinum, gallium and sodium, zirconium and yttrium,zirconium and erbium, zirconium and chromium, zirconium and manganese,zirconium and iron, zirconium and platinum, manganese and sodium,manganese and yttrium, manganese and titanium, manganese and chromium,manganese and iron,-manganese and nickel and palladium and iron. Theforegoing is not an exhaustive list.

The invention is distinguished from prior expedients to mitigate smokeformation in that substantially none of the catalyst is found in thecombustion gases. Moreover, the combustion of flames in contact withmaterials which are catalytically active for reducing smoke haspreviously been carried out with the said materials contacting eitherthe whole flame or the secondary zon'e thereof, but it has notpreviously been proposed that contact between the flame and anyparticular material or materials shouldbe confined to the primaryreaction zone of the flame.

It is preferred that the catalyst be located within the primary reactionzone as far as possible upstream from the secondary reaction zone, andnear to, but within the base of the flame, so that the risk of contactof the secondary zone withthe catalyst is minimized.

Depending on the physical nature of the catalyst, and the type ofequipment with which it is to be used, the catalyst may be provided inthe form of wires or a planar mesh or grid, or a flat spiral, orcylindrical coil, of wires or a perforated screen, the wires or screenbeing either of the catalyst itself or of a supporting material which iscomposited with or on which is coated the catalyst. Alternatively thecatalyst may be impregnated onto asbestos or like flame resisting porousmaterial. A convenient method'of making the supported form of catalystis to impregnate the support with a solution of a suitable metalcompound, dry the impregnated support of solvent and to heat the supportuntil the metal compound or a heat stable derivative thereof iseffectively bound to the support.

However, it is-preferred wherever'possible that the form in which thecatalyst is provided should be such 3 that it causes a minimum ofdisturbance to the flow of fuel and air and to the general aerodynamicsof the flame.

The benefits arising from the invention include, as a result of the useof less excess air than would otherwise necessarily be the case, notonly a higher thermodynamic efficiency, but also the possibility ofburning fuel at greater rates without producing smoke in a given volume,and thereby increasing the maximum power output from a boiler, furnaceor engine. In addition, when the fuel employed contains sulphur (whichis usually the case), the reduced excess air reduces the proportion ofcorrosive sulphur trioxide in the combustion gases which is produced byoxidation of sulphur dioxide: similarly, because there is less excessair, the proportion of undesirable oxides or nitrogen tends to bereduced.

The invention will now be illustrated by reference to the accompanyingdrawings in which:

FIG. 1 illustrates diagrammatically a method of locating the variousreaction zones of a flame.

FIG. 2 illustrates schematically an apparatus employed forinvestigations in connection with the present invention.

FIG. 3 shows an investigation in connection with this invention beingeffected using the apparatus of FIG. 2.

FIG. 4 is a cross-sectional elevational view of the principal parts of adomestic central heating burner.

FIG. 5 is a perspective view ofa flame plate assembly forming part ofthe burner of FIG. 4.

FIG. 6 shows perspectively a mesh or grid of catalytically activematerial for use with the burner of FIG. 4.

FIG. 7 shows the lower part of the burner of FIG. 4 and the generalstructure of a typical flame therefrom.

FIG. 8 shows a conventional refinery flare stack.

FIG. 9 is a perspective view of a form of catalyst for use with refineryflares.

FIG. 10 depicts perspectively the embodiment of FIG. 9 mounted on arefinery ground flare or stack, and

FIG. 11 illustrates the mode of action of the embodiment of FIG. 10.

Referring first to FIG. 1, there is shown a burner tube through which afuel, such as an inflammable gas, is passed. The gas is combusted toform a flame 23 and electrodes 21, 22 are located with their free endsin diametrically opposed parts of the visible edge of the flame 23.

The ends of the electrodes 21, 22 are rounded to a known radius so thatthe area of electrode available for ion collection is known: a suitableradius is 0.5 mms. for electrodes I mm. diameter. A voltage is appliedacross the flame 23 from the electrodes 21, 22, the voltage beingsupplied from a battery 24 and regulated by a tapping 25 of apotentiometer 26. The voltage is measured by a voltmeter 27 and thecurrent passing through the flame by a micro-ammeter 28.

The voltage applied across the flame 23 is progressively increased foreach location of the flame until a saturation current is reachedindicating that for that location, the maximum current for the ionicconcentration has been reached. The current direction is reversed by aswitching device (not shown) to compensate for any assymmetry in theflame, and the procedure repeated. The whole procedure so far describedis repeated for a number of positions of the electrodes 21, 22 in theflame 23 until a profile of the ion concentration for the flame can beconstructed.

It is found that the region of the flame nearest to the burner tube 20,apart from a cool fuel and air mixing zone 29 has the highest ionconcentration, this being the so-called primary reaction zone. Theprimary reaction zone is always adjacent to the base of the flame 23,and terminates fairly abruptly at locations distal from the base of theflame: the region of the flame which is furthest from the base of theflame is found to be of low conductivity, and contains the most luminouspart of the flame.

Referring now to FIG. 2, tests were performed using an uprightlaboratory burner 30 which burned ethylene in air. Ethylene from acylinder (not shown) was supplied via line 31 and a regulating valve 32to a flow measuring device 33 of the type known as a rotameter, and thento a mixing line 34 wherein was mixed with a small proportion of airsupplied from line 35, valve 36 and rotameter 37. The rate of flow ofair was kept constant, while the rate of flow of ethylene-air mixturewas regulated by valve 38 and measured by a rotameter 39. The mixturewas burned in a flame 40 at the top of the burner 30 with a known amountof secondary combustion air supplied to a glass tube 41 surrounding theburner 30 from a line 42. The secondary combustion air flow rate wasregulated by a valve-43 and monitored by a rotameter 44. A glass tube 45surrounded the tube 41 and extended a considerable distance above theflame 40 to shield the flame 40 from draughts.

In the flame 40, the various zones found by the method described inrelation to FIG. 1 are indicated by I which is the primary reaction zoneextending from the cool base of the flame at the top of the burner 30,II which is the secondary reaction zone which, with the cool zone,sandwiches the primary reaction zone, and III a cooler tertiary zonewherein smoke (if any) tends to be visible to the eye. The various zonesof the flame 40 are not intended to be shown in the correct relativesizes in FIG. 2.

FIG. 3 shows a test for smoke mitigation in accordance with theinvention using the apparatus of FIG. 2. The test procedure is asfollows in a typical case, given by way of Example.

EXAMPLE 1 Test (a) Ethylene gas from the cylinder (not shown) was passedthrough the rotameter 33 of FIG. 3, premixed with a small known fixedflow rate of air measured by the rotameter 37 of FIG. 2 and passed tothe barrel of the upright tubular burner 30. A measured fixed flow rateof secondary combustion air was passed into the annular space betweenthe burner 30 and the glass tube 41, and maintained throughout the testsat 400 cc s/minute.

The ethylene-air mixture'was ignited at the top of the burner and it wasfound that with 21.5 ccs per minute of air, about 94 ccs per minute ofethylene in the ethylene-air mixture could be burned before smoke wasjust visually detectable at the top of the flame (zone III of FIG. 2).

The effect of a catalyst in accordance with the invention was nowinvestigated. The chosen catalyst was barium oxide coated onto acircular filament of quartz at one end of a quartz rod, as depicted inFIG. 3.

Test (b) The quartz rod 46 with the filament 47 at its end was solocated that the coated filament was within the yellow luminoussecondary reaction zone (zone II of FIG. 2) of the flame 40. The flamebegan to smoke copiously and the flow-rate of ethylene was reducedgradually (using the control valve 32 of FIG. 2) until the smoking hadvirtually ceased. It was found that the flow-rate of ethylene was nowabout 64 ccs per minute as measured by the rotameter 33 of FIG. 2.

When the coated filament 47 was removed from the flame, the smokingdisappeared, and the flow-rate of ethylene could be increased to about94 ccs per minute before smoking was once again just detectable.

Test (c) The coated filament 47 was positioned within the flame justabove the barrel of the burner tube 30 and in the bluish-colouredprimary reaction zone (zone I of FIG. 2).

No smoke was at all discernible at the ethylene flowrate of 94 ccs perminute, and the ethylene flow-rate was gradually increased by openingthe valve 32 of FIG. 2 until smoke was just detectable: the flow-ratewas then about 137 ccs per minute.

When the coated filament 47 was removed from the flame, smoking was verymarked and did not substantially cease until the ethylene flow-rate hadbeen reduced once again to 94 ccs per minute.

Test ((1) The coated filament 47 was located at the top (zone III ofFIG. 2) of the visible flame with an ethylene-air flow rate of 94 ccsper minute. No effect on the amount of smoke was observed, and anincrease in the ethylene flow rate increased the amount of smoke in thesame way as in the absence of the filament 47.

The tests (a) (d) demonstrate that to attain the limit of smokeformation, the combustible fuel could be increased by about 37% by theembodiment of the invention relative to the premixed ethylene-airflow-rate which gave a flame just at the limit of smoke productron.

The tests (a), (b), (c) and (d) illustrate the criticality of thelocation of the catalyst in the flame. The tests also demonstrate in asimple way that by the practice of the invention, the proportion ofexcess air in relation to the fuel consumed necessary for thesatisfactory combustion of a fuel can be reduced thus improving theefficiency of combustion.

Results which were qualitatively similar to those of tests (a), (b), (c)and (d) were obtained in tests employing all the isomers of butene,isoand nbutanes, kerosine, gas oil and petroleum gases, and the benefitsof the invention were realized both with diffusion and premixed flames,and partially premixed and diffusion flames. In every case, it was foundthat the practice of the invention enabled 30-60% more fuel to be burnedwithout any increase in smoke or in secondary air.

EXAMPLE 2 The test of Example 1 were performed again but with ethylenepremixed with a fixed quantity of air (from line 35 in FIG. 2), the airflow rate being again 21.5 ccs/minutes, and the amount of secondary airagain being fixed at a flow-rate of 400 ccs/minute.

The filament 37 of FIG. 3 was coated with different metal oxides in eachtest, and starting with an ethylene flow-rate of 94 ccs/minute to give aflame in which smoke formation was about to occur at the top, thepercentage increase in the rate of ethylene flow with each coatedfilament located in the primary reaction zone of the flame, relative tothe fuel flow rate in the absence of the coated filaments, being noted.

The results are summarized in Table 1.

The results given in Table 1 show gallium oxide to be the best filamentcoating followed closely by the noble metals platinum and palladium.

The same pattern of results was obtained in other experiments usingdiffusion, pre-mixed and partially premixed flames with otherhydrocarbon gases as fuels, although the actual percentage increase insmoke-limited fuel flow-rate was not in each case the same.

From the point of view of cost, availability and effectiveness, themetal oxides which prima facie appear to be of greatest potential forordinary or commercial usage are barium and sodium. However, sincesodium oxide is relatively more volatile than barium oxide (although theactual volatility is very small), further experiments, as hereinafterdescribed, were performed using barium.

EXAMPLE 3 A number of tests were performed employing the burner of acommercially available high efficiency domestic boiler consuming lightfuel oil.

The burner is shown in FIG. 4 and was of the downwardly-firing type thatis to say, the flame extended downwards from the burner. The burner 50comprised a fuel pump 51, a central tube 52 for the fuel whichterminated at its lower-most end in a nozzle 53 having number of fineorifices for atomising the fuel, a centrifugal fan 54 for supplyingprimary combustion air and a concentric tube 55 for primary combustionair surrounding the fuel tube 52. The concentric tube 55 extendedslightly lower than the central fuel tube 52, and a flame plate extendedacross the bottom of the air and fuel tubes 55, 52 respectively.Ignition of the mixture of air and atomized fuel was effected by meansof an electrode 56 carried by an insulated support. The flame plate isshown in more detail in FIG. 5 and comprises an outer support ring 57,which is a close fit in the end of the air tube 55, and a number ofinwardly extending blades 61 which are generally radial but which do notmeet at the axis of the support ring 57. The blades 61 are slightlycurved in cross-section so that they impart a swirling motion to the airpassing through the flame plate and thereby promote good mixing of thefuel and air. The flame plate is supported by a number of struts 64which extend from the upper side of the support ring 57 to a fixed ringlocated around the fuel tube 52.

The burner 50 is set into a refractory wall 58 at its downstream side,and a stout strut 59 attached to the outside of the air tube 55 provideslateral support for the burner 55.

A catalytically active grid 66, shown in FIG. 6, was made up by formingin a ring 60 of 4% inches diameter a refractory mesh or network of 1/16inch thick wire like members forming individual rectangles of 1 inch by72 inch. A layer of barium oxide was coated on the wires of the grid tobring the thickness of the wires to about 7% inch. On diametricallyopposite outer sides of the ring 66 were provided supporting lugs havinginternally threaded holes for the receipt of locating screws.

The burner was ignited in the normal way and the air flow rate wasmonitored. During normal operation, the excess air was found to be about20% for the selected fuel flow-rate.

Flg. 7 shows the general form of flame produced below the burner. Theflame base was located about Vs inch below the flame plate, and theflame itself extended about -12 inches below the flame plate and was 3%to 4 inches in diameter, In contrast to the ethylene flame of Examples 1and 2, the relatively high velocity of the swirling fuel and air mixturepassing from the flame plate made the primary reaction zone boundariessomewhat indeterminate by visual observation, but it was expected thatthe primary reaction zone would not extend much more than about 1% 1%inches from the flame plate, the secondary reaction zone accounting formost of the rest of the flame. These expectations were confirmed to asatisfactory degree by electrical conductivity determinations along thelines discussed in relation to FIG. 1.

Without changing the fuel or air flow-rates, the catalyst grid 66 ofFIG. 6 was disposed in the flame at various distances from the flameplate, which was used as a reference for distance. As will be seen fromFIG. 7, the burner support wall 58 is provided with apertures throughwhich depend captive screws 69 held in position by washers 70 around aneck of the screws 69. The captive screws 69 are so arranged that theycan engage with the threaded holes in the lugs 68 of the grid 66 and byrotation of the screws 69, the distance between the plane of the mesh ornetwork of coated wires 67 and the flame plate can be adjusted.

The amount of smoke generated by the flame was determined by theStandard Bacharach test.

The results of the test are summarized in the following table, in whichthe column headed distance refers to the distance from the flame plate.

The results in the table demonstrate that a marked reduction in smokeand hence an improvement in fuel utilization is obtained by disposingthe catalyst near the base of the flame (i.e., near the flame plate),and in the region of the primary reaction zone of the flame.

When test No. 2 of the table was repeated with varying quantities ofair, it was found that the excess air requirement could be reduced fromthe normal value of 20% to 1 1% before a Bacharach smoke No. 3, equal tothe normal smoking tendency of the burner, was obtained.

Apart from the increase in thermal and thermodynamic efficiency providedby the decrease in excess air from 20% to 11%, it would be expected thatthere would also be areduction in the concentration of sulphur trioxidein the combustion gases of nearly 60%, and a reduction in theconcentration of nitrogen oxides of about 13%.

Although the above tests of Example 3 were performed on a domesticboiler, it will be appreciated that the benefits of the invention can berealized on larger boilers, and that due to the lower excess airrequirements, benefits such as smaller air fans, pipes and combustionchambers can be realized with considerable savings in cost. Thereduction in SO concentration would be beneficial in respect of lesscorrosion, and in nitrogen oxides in less atmospheric pollution. Inaddition, the decrease in smoke would of course lead to less frequentshut-downs of industrial plant for cleaning.

There are some instances in the combustion of carbon-containingmaterials in which it is not necessary to attempt to attain the highestcombustion temperatures but it is desirable to mitigate the amount ofsmoke formed during combustion. Among these instances may be cited byway of example the combustion of waste hydrocarbon or fuel gases frompetroleum refinery and blast furnace operations and the combustion ofhydrocarbons or fuel gases in the firing of lime and in some ceramic andbrick production processes.

A particularly useful application of the invention is to the mitigationof smoke formation in the burning of petroleum refinery wastehydrocarbon gases. These gases are of variable composition and theirquantity often varies: accordingly, they have little value and theirdisposal is most simply accomplished by burning them in flares which arecommonly at the top of tall flare stacks, and sometimes nearer to theground on socalled ground stacks.

There is a marked tendency for the burning of refinery gases in flaresto cause serious smoke formation. I-Ieretofore, the smoke formation hasbeen mitigated at least to some extent by injecting steam into theflare. For a satisfactory degree of effectiveness, relatively largequantities of steam are required for example, from 1 to 3 lbs. of steamfor each 1 lb. of refinery gas, and it will be appreciated that themitigation of smoke formation by this expedient is expensive. Inaddition, steam injection is very noisy.

FIG. 8 shows the essential features of a conventional flare stackarrangement wherein the stack 81 is supplied with waste refinery gasesby a trunking 82, and the gases are burned in a flame 84 at the top ofthe stack 81. The flame may be 60 feet in length, sometimes more, anymay produce large quantities of smoke, depending on the composition ofthe gases. For steam injection, steam is injected into the stack 81through a trunking 83.

One form of catalyst for refinery flare use in accordance with theinvention is a cylindrical coil of alumina-silica material previouslyimpregnated with a mixture of barium and sodium compounds such as bariumnitrate and sodium hydroxide and fired to convert the barium nitrate tobarium oxide and to dehydrate to some extent, the sodium hydroxide tosodium oxide which combines with the ceramic. It has been found that thecylindrical coil stablized flames, and promoted the induction into theflare flame of secondary air which enhanced the smoke reducing activityof the barium, sodium and alumina containing coil.

A suitable cylindrical coil 90 is shown in FIG. 9.

Preferably, the coil has a mean diameter slightly exceeding the diameterof the flare exit, and a length preferably no greater than 20% of thatof the expected mean length of the flame and more preferably, up to ofthe flame length.

EXAMPLE 4 In a qualitative experimental simulation of the application ofthe invention to flare stack operation, a tube of approximately 1%inches internal diameter represented the flare stack, and the fuel was amixture of saturated hydrocarbon gases known in the art as LPG(liquified petroleum gas) enriched with propene to cause smokeformation. The rate of gas flow was so adjusted that a smokey flamehaving a height of 4 to 5 feet was obtained.

A cylindrical barium/sodium/silica-alumina coil made as described abovehaving the form shown in FIG. 9 with dimensions of about 1% inchesinternal diameter and about 9 inches long was inserted into the base ofthe flame. A number of human observers subjectively estimated that smokeintensity was almost halved. Additionally, it was noted that the flamewas considerably more stable with the coil in the flame than before thecoil was disposed in the flame. When the coil was removed from theflame, the smoke intensity was estimated to be about the same as beforethe insertion of the coil.

Although the experimental simulation described above was effected instill air conditions, the invention is useful in windy conditions whenthe axis of the flame is inclined to the vertical or even substantiallyhorizontal. For the most advantageous effect, it is preferred that thecatalyst coil be mounted, e.g., on gimbals, for rotational movementabout a vertical axis and rotational movement about a horizontal axis,there being at least one wind vane device attached directly orindirectly to the catalyst coil to maintain the catalyst coil within theprimary reaction zone of the flame and with the axis of the coil and theflame substantially coincident.

It is preferred that the bearings of the gimbals or other mounting belocated well clear of the flame, and it is advantageous to provide onewind vane device responsive to horizontal directional changes in windmotion and one wind vane device responsive to vertical directionalchanges in wind motion. It is preferred that the wind vane devices be solocated that they will be clear of the flame at substantially all time.FIG. 9 illustrates a way of applying the practice of the invention torefinery flares, and the stack 81 may be of the type shown in FIG. 8 orit may be of the ground flare type.

Attached near the top of the stack 81 is a collar 91 on which isrotatably mounted a ring 92 which is suitably separated from the collar91 by bearings, diagrammatically shown as rollers 93. It is alsopreferred to provide bearings (not shown) between the ring 92 and thestack 81. The form of the appropriate bearings will be clear to thoseskilled in the art.

A wind vane 94 responsive to changes in the horizontal component of winddirection is attached to the ring 92 so that changes in wind directionin horizontal planes cause rotation of the ring 92. At right angles tothe direction of the vane 94, there are provided stub axles 95 whichproject outwardly from the ring on diametrically opposed sides thereof.Each stub axle 95 serves to support in a recessed journal-bearing a rod96 having a bearing collar 97. At the bottom end of each rod 96 is acounterweight 98 which serves to maintain the rod 96 in the positionillustrated. A wind vane 99 is formed in each rod 96 above the collar97, the vanes 99 being at right angles to the vane 94 and responsive tochanges in the vertical components of wind direction.

A coil 90, of the type illustrated in FIG. 9, is located relative to thestack 81 by horizontal rods extending inwardly from the tops of rods 96,the rods 100 being attached to the coil 90.

In the absence of wind, the flare flame encloses the coil 90 and burnsvertically, the coil 90 helping to diffuse air into the flame andadditionally stabilizing the flame. The mitigation of smoke may be sogreat that steam injection may be dispensed with entirely.

In the presence of wind tending to tilt the flare flame, as shown inFIG. 11, the vane 94 causes the ring 92 to rotate to a position in whichthe vanes 99 are substantially perpendicular to the wind direction, andthe wind, then acting on the vanes 99 against the action of thecounterweights 98, causes the coil 90 to be tilted substantially intothe flame 101. To a substantial extent, the flame stabilizes around thecoil, and, by the principles of the present invention, smoke produced bythe flame is substantially reduced or eliminated.

Although the invention has been most specifically described by referenceto FIGS. 8-10 in relation to petroleum refinery flare stack flames, itwill be appreciated that it may be applied to other flames where smokeformation is to be mitigated.

EXAMPLE 5 The experiments described in examples 1 and 2 and illustrateddiagrammatically in FIGS. 2 and 3 were performed with mixtures of metaloxides coated on the quartz filament 47. The fuel was again ethylenepremixed with a fixed flow-rate of air (21.5 ccs per minute) and with afixed flow-rate of secondary air (400 ccs per minute). i

The percentage fuel flow increase for a number of mixed metal oxidecoatings on the filament 47 before smoke was discernable was noted, andthe results are summarized in Table 2.

TABLE 2-continued When the results of Tables 1 and 2 are compared, it isclear that the mixtures of metal oxides give superior results to the useof single metal oxides alone and that a synergistic interaction takesplace in the case of mixed metal oxides.

Accordingly, it is yet another aspect of this invention that a mixtureof metal oxides, such as the mixtures disclosed in table 2, are locatedin the primary reaction zone of the flame of a domestic or industrialburner, or in the flame of a refinery gas flare, or in the flames fromblast furnace gases or flames for the firing of limestone, ceramics andbricks.

The invention is also useful in engines wherein there is a reasonabledegree of definition of the primary reaction zone of the flame e.g., inexternal combustion engines and in the cans of the combustion chambersof gas-turbine engines. The invention may also be useful in certaintypes of diesel engine wherein the initial combustion of the fuel iseffected in a cell which is separated from the main combustion chamber.

What is claimed is:

1. A method of improving the combustion of a carbon-containing fuel in aflame, comprising fixedly disposing in the primary reaction zonecharacterized by the flame having its highest ion concentration, a solidmaterial which is catalytically active for reducing smoke and which issubstantially involatile at the temperature of the primary reactionzone, wherein the catalytically active material is selected from thecombination of compounds of barium and sodium, barium and yttrium,barium and erbium, barium and zirconium, aluminium and sodium, aluminiumand yttrium, aluminium and lanthanum, aluminium and erbium, aluminiumand platinum, gallium and sodium, zirconium and yttrium, zirconium anderbium, zirconium and chromium, zirconium and manganese, zirconium andiron, zirconium and platinum, manganese and sodium, manganese andyttrium, manganese and titanium, manganese and chromium, manganese andiron, manganese and nickel and palladium and iron.

2. A method according to claim 1 in which the catalytically activematerial is selected from the following metal and metal compounds:barium, magnesium, iron, tin, aluminium, vanadium, manganese, sodium,calcium, zirconium, platinum, yttrium, lanthanum, erbium, gallium,titanium, chromium, cobalt, nickel, palladium, a rare earth metal,oxides of any of said metals, compounds of said metals which decomposeto oxides 12 under the action of heat, and heat stable compounds of saidmetals.

3. Apparatus for burning a carboncontaining fuel comprising means forthe supply of a carboncontaining fuel to a combustion zone wherein thefuel is burned in a flame having a primary reaction zone characterizedby the flame having its highest ion concentration and a secondaryreaction zone having low ion concentration relative to said primaryzone, and a solid catalytically active material located in the primaryreaction zone of the flame, said solid material being active forreducing smoke and being substantially involatile at the temperature ofthe primary reaction zone, wherein the catalytically active material isa compound selected from compounds of barium and sodium, barium andyttrium, barium and erbium, barium and zirconium, aluminium and sodium,aluminium and yttrium, aluminium and lanthanum, aluminium and erbium,aluminium and platinum, gallium and sodium, zirconium and yttrium,zirconium and erbium, zirconium and chromium, zirconium and manganese,zirconium and iron, zirconium and platinum, manganese and sodium,manganese and yttrium, manganese and titanium, manganese and chromium,manganese and iron, manganese and nickel and palladium and iron.

4. Apparatus according to claim 3 in which the catalytically activematerial is selected from the following metal and metal compounds:barium, magnesium, iron, tin, aluminium, vanadium, manganese, sodium,calcium, zirconium, platinum, yttrium, lanthanum, erbium,gallium,'titanium, chromium, cobalt, nickel, palladium, oxides of any ofsaid metals which decompose under the action of heat to the oxide.

5. Apparatus for burning a carboncontaining fuel comprising means forthe supply of a carboncontaining fuel to a combustion zone wherein thefuel is burned in a flame having a primary reaction zone and a secondaryreaction zone, and a solid material having at least part located in theflame, at least a major portion of said part being located in theprimary reaction zone of the flame, the said solid material beingcatalytically active for reducing smoke and being substantiallyinvolatile at the temperature of the primary reaction zone, saidcatalytically active material being in the form of a substantiallycylindrical spiral having a mean diameter slightly smaller than the meandiameter of the primary reaction zone.

6. Apparatus according to claim 5 in which the fuel is a gaseous fueland the said means for the supply of fuel to the combustion zonecomprises an upstanding tube having an outlet for gaseous fuel at thetop, the said substantially cylindrical spiral being mounted relative tothe tube on supports permitting movement of the spiral in threedimensions, and there being means responsive to the wind direction inthe vicinity of the top of the tube for causing movement of the spiralrelative to the top of the tube whereby the axis of the tube issubstantially maintained coaxial with the axis of the flame formed bycombustion of the fuel at the top of the tube.

7. Apparatus according to claim 6 in which the said means responsive tothe wind direction comprise vanes

1. A METHOD IF IMPROVING THE COMBUSTION OF A CARBON-CON TAINING FUEL INA FLAME, COMPRISING FIXEDLY DISPOSING IN THE PRIMARY REACTION ZONECHARACTERIZED BY THE FLAME HAVING ITS HIGHEST ION CONCENTRATION, A SOLIDMATERIAL WHICH IS CATALYTICALLY ACTIVE FOR REDUCING SMOKE AND WHICH ISSUBSTANTIALLY INVOLATILE AT THE TEMPERATURE OF THE PRIMARY REACTIONZONE, WHEREIN THE CATALYTICALLY ACTIVE MATERIAL IS SELECTED FROM THECOMBINATION OF COMPOUNDS OF BARIUM AND SODIUM, BARIUM AND YTTRIUM,BARIUM AND ERBIUM, BARIUM AND ZIRCONIUM, ALUMINIUM AND SODIUM, ALUMINUMAND YTRIUM, ALUMINUM AND LANTHANUM, ALUMINUM AND ERBIUM, ALUMINUM ANDLATINUM, GALLIUM AND SODIUM, ZIRCONIUM AND YTTRIUM, ZIRCONIUM ANDERBIUM, ZIRCONIUM AND CHROMIUM, ZIRCONIUM AND PLATINUM, MANGANESEZIRCONIUM AND IRON. ZIRCONIUM AND PLATINUM, MANGANESC AND SODIUM,MANGANESE AND YTTRIUM, MANGANESE AND IRON, MANGANESE MANGANESE ANDCHROMIUM, MANGANESE AND IRON, MANGANESE AND NICKEL AND PALLADIUM ANDIRON.
 2. A method according to claim 1 in which the catalytically activematerial is selected from the following metal and metal compounds:barium, magnesium, iron, tin, aluminium, vanadium, manganese, sodium,calcium, zirconium, platinum, yttrium, lanthanum, erbium, gallium,titanium, chromium, cobalt, nickel, palladium, a rare earth metal,oxides of any of said metals, compounds of said metals which decomposeto oxides under the action of heat, and heat stable compounds of saidmetals.
 3. Apparatus for burning a carboncontaining fuel comprisingmeans for the supply of a carboncontaining fuel to a combustion zonewherein the fuel is burned in a flame having a primary reaction zonecharacterized by the flame having its highest ion concentration and asecondary reaction zone having low ion concentration relative to saidprimary zone, and a solid catalytically active material located in theprimary reaction zone of the flame, said solid material being active forreducing smoke and being substantially involatile at the temperature ofthe primary reaction zone, wherein the catalytically active material isa compound selected from compounds of barium and sodium, barium andyttrium, barium and erbium, barium and zirconium, aluminium and sodium,aluminium and yttrium, aluminium and lanthanum, aluminium and erbium,aluminium and platinum, gallium and sodium, zirconium and yttrium,zirconium and erbium, zirconium and chromium, zirconium and manganese,zirconium and iron, zirconium and platinum, manganese and sodium,manganese and yttrium, manganese and titanium, manganese and chromium,manganese and iron, manganese and nickel and palladium and iron. 4.Apparatus according to claim 3 in which the catalytically activematerial is selected from the following metal and metal compounds:barium, magnesium, iron, tin, aluminium, vanadium, manganese, sodium,calcium, zirconium, platinum, yttrium, lanthanum, erbium, gallium,titanium, chromium, cobalt, nickel, palladium, oxides of any of saidmetals which decompose under the action of heat to the oxide. 5.Apparatus for burning a carboncontaining fuel comprising means for thesupply of a carboncontaining fuel to a combustion zone wherein the fuelis burned in a flame having a primary reaction zone and a secondaryreaction zone, and a solid material having at least part located in theflame, at least a major portion of said part being located in theprimary reaction zone of the flame, the said solid material beingcatalytically active for reducing smoke and being substantiallyinvolatile at the temperature of the primary reaction zone, saidcatalytically active material being in the form of a substantiallycylindrical spiral having a mean diameter slightly smaller than the meandiameter of the primary reaction zone.
 6. Apparatus according to claim 5in which the fuel is a gaseous fuel and the said means for the supply offuel to the combustion zone comprises an upstanding tube having anoutlet for gaseous fuel at the top, the said substantially cylindricalspiral being mounted relative to the tube on supports permittingmovement of the spiral in three dimensions, and there being meansresponsive to the wind direction in the vicinity of the top of the tubefor causing movement of the spiral relative to the top of the tubewhereby the axis of the tube is substantially maintained coaxial withthe axis of the flame formed by combustion of the fuel at the top of thetube.
 7. Apparatus according to claim 6 in which the said meansresponsive to the wind direction comprise vanes attached to the saidsupports.